There are several hundred thousand tons of polyolefin-polystyrene block copolymers, such as styrene-ethylene/butylene-styrene (SEBS) or styrene-ethylene/propylene-styrene (SEPS) in the global market therefor. In addition, these are excellent in thermal and light resistance compared to the styrene-butadiene-styrene (SBS) or styrene-isoprene-styrene (SIS), and are used as a material for a grip and a handle with soft and good textures, a flexible material for diapers, oil-gel used for medical and communication materials, an impact modifier in engineering plastic, or a flexibilizer or toughener in transparent polypropylene. Conventional SEBS is prepared through a two-step reaction of hydrogenating SBS obtained by anionic polymerization of styrene and butadiene. Conventional SEPS is also prepared through a two-step reaction of hydrogenating SIS obtained by anionic polymerization of styrene and isoprene. Since such a process of saturating all double bonds contained in the main chain of a polymer through hydrogenation has a high production cost, the unit costs of SEBS and SEPS are considerably higher than those of SBS and SIS before hydrogenation. Such a reason may act as a limit to market expansion. In addition, since it is actually impossible to saturate all of the double bonds contained in the polymer chain through hydrogenation, commercialized SEBS and SEPS contain some remaining double bonds and the presence of the double bonds often become a problem (Journal of Polymer Science: Part A: Polymer Chemistry, 2002, 40, 1253; Polymer Degradation and Stability 2010, 95, 975). Moreover, the conventional block copolymer prepared in the two steps as described above is very limited in structure because a polyolefin block is formed by hydrogenation after anionic polymerization of butadiene or isoprene.
According to such background, the preparation of a polyolefin-polystyrene block copolymer directly through a one-pot reaction from an olefin monomer and a styrene monomer is a very challenging research topic with a large commercial ripple effect. In this context, conventionally, it has been reported that a polypropylene-polystyrene block copolymer is prepared by synthesizing polypropylene having a para-methylstyryl group at a terminal end using para-methylstyrene as a chain transfer agent in propylene polymerization from para-methylstyrene, inducing dehydrogenation of a methyl group at the terminal end using butyl lithium, and then performing anionic polymerization of styrene (J. Am. Chem. Soc. 2001, 123, 4871; Macromolecules 2002, 35, 1622). It also has been reported that there is an attempt to prepare a block copolymer by performing ethylene/propylene copolymerization using living polymerization reactivity of a phenoxyimine catalyst and subsequently injecting a styrene monomer (Macromole. Rapid. Commun., 2006, 27, 1009). However, the conventionally reported methods described above have problems of requiring multi-step processes, and thus may not be applied to a commercial process.